Medical hollow tube

ABSTRACT

A cable includes a sheath, and a coating film covering a circumference of the sheath. The coating film adheres to the sheath. The static friction coefficient of a surface of the coating film is smaller than the static friction coefficient of a surface of the sheath. The adhesion strength between the sheath and the coating film is 0.30 MPa or more.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a Continuation of U.S. patent applicationSer. No. 16/411,709 filed May 14, 2019 which is based on Japanese patentapplication No. 2018-95112 filed on May 17, 2018, Japanese patentapplication No. 2018-162773 filed on Aug. 31, 2018, and Japanese patentapplication No. 2019-82944 filed on Apr. 24, 2019, the entire contentsof which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a cable and a hollow tube for medicaluse, and to a technique effective in applying to, for example a probecable connectable to a medical device or a hollow tube such as a tubeinto which a catheter is inserted.

2. Description of the Related Art

JP-A-2008-287 describes a technique relating to a medical coatingcomposition capable of imparting stable slidability without applying alubricant to a surface.

SUMMARY OF THE INVENTION

The surface of the cable is formed with a sheath thereover made of aninsulating member. It is desired that this sheath has no stickiness andthe like and has a good sliding property (slidability). On the otherhand, an end portion of the cable is processed in such a manner as toattach a protective member such as a boot to the sheath with anadhesive. Here, in the cable to which the protective member is attached,for example, when the end portion of the cable is bent, a coating filmformed over the surface of the sheath peels off, and the protectivemember may come off the cable. That is, the cable is required to have nostickiness over the surface of the cable, to have a good slidingproperty, and to be formed with the coating film over the surface of thesheath being unlikely to peel off.

The cable in one embodiment comprises a sheath and a coating filmcovering a circumference of the sheath and adhering to the sheath. Atthis time, a static friction coefficient of the surface of the coatingfilm is smaller than a static friction coefficient of the surface of thesheath, and an adhesion strength between the sheath and the coating filmis 0.30 MPa or more.

The hollow tube for medical use according to one embodiment includes ahollow tube body and a coating film covering at least one of an innersurface and an outer surface of the hollow tube body and adhering to thehollow tube body. At this time, a static friction coefficient of thesurface of the coating film is smaller than a static frictioncoefficient of the surface of the hollow tube body, and an adhesionstrength between the hollow tube body and the coating film is 0.30 MPaor more.

(Points of the Invention)

According to one embodiment, it is possible to provide the cable whichhas no stickiness over the surface of the cable, has a good slidingproperty, and which is formed with the coating film over the surface ofthe sheath being unlikely to peel off.

According to one embodiment, it is possible to provide the hollow tubefor medical use which has no stickiness over the surface of the hollowtube, has a good sliding property and which is formed with the coatingfilm over the surface of the hollow tube body being unlikely to peeloff.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram showing a probe cable connectable to anultrasonic imaging device;

FIG. 1B is a cross sectional view of the probe cable along A-A line;

FIG. 2 is a diagram showing a configuration example in which a coatingfilm is formed over a surface of a sheath;

FIG. 3 is a diagram showing a schematic configuration of a coating filmin an embodiment;

FIG. 4 is a diagram for explaining the difference between siliconerubber, silicone resin, and silica;

FIG. 5 is a schematic diagram showing that the density of the voids inthe silicone rubber constituting the parent material of the coating filmis larger than the density of the voids in the silicone rubberconstituting the sheath;

FIG. 6 is a schematic diagram showing that the density of the voids inthe silicone rubber constituting the parent material of the coating filmis equal to the density of the voids in the silicone rubber constitutingthe sheath;

FIG. 7 is a diagram for explaining a method of producing an evaluationsample for evaluating the adhesion strength between the sheath and thecoating film;

FIG. 8 is a schematic diagram showing a measuring method for measuringthe tensile shear strength using the sample for evaluation;

FIG. 9 is a schematic diagram showing a bending resistance test of aprobe cable;

FIG. 10A is a cross sectional view of a hollow tube for medical useincluding a hollow tube body and an outer coating film on an outersurface of the hollow tube body;

FIG. 10B is a cross sectional view of a hollow tube for medical useincluding a hollow tube body and an inner coating film on an innersurface of the hollow tube body; and

FIG. 10C is a cross sectional view of a hollow tube for medical useincluding a hollow tube body, an outer coating film on an outer surfaceof the hollow tube body and an inner coating film on an inner surface ofthe hollow tube body respectively.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In all the drawings for explaining the embodiments, the same members aredenoted by the same reference numerals in principle, and the repetitivedescriptions thereof will be omitted. Note that even in a plan view,hatching may be added to make the drawings easy to understand.

<Review of Improvement>

For example, in cables used for medical applications, importance isplaced on handling of probes in inspection. Specifically, polyvinylchloride (PVC) is used for the sheath of the cable, but as the useperiod becomes longer, a phenomenon such as discoloration occurs in thesheath made of the PVC. From this fact, it is considered that siliconerubber excellent in heat resistance and chemical resistance is used asthe sheath particularly for cables used for medical applications.

However, the sheath made of silicone rubber has a sticky nature(so-called “tack”, “tackiness”, or the like), the sliding property(slidability) is not excellent. Therefore, when the silicone rubber isapplied to the sheath of the cable, there arises the problem that it iseasy for the cable to be caught in other members, and that dust is alsoeasy to adhere to the surface of the cable. In particular, when thecable is easily caught in other members, for a probe cable connected toa medical device (e.g., an ultrasonic imaging device), handling of thecable becomes difficult. This is because, in the ultrasonic imagingdevice for example, since inspection is performed while moving theultrasonic probe connected to the probe cable on the human body, theprobe cable is easily caught in the cables or in clothes or the like andit becomes impossible to move the ultrasonic probe smoothly. Therefore,in cables used for medical applications, it is desired that the cabledoes not have the tack and that the surface of the cable has a goodsliding property (slidability).

Regarding this point, in order to realize a highly slidable cable withthe reduced tack of the surface, it is necessary to reduce thefrictional resistance of the surface of the cable, and as means forreducing the frictional resistance of the surface of the cable, it hasbeen studied that a coating film with a low static friction coefficientis formed over the surface of the sheath. However, according to thestudy of the present inventor, it is found that when the coating filmhaving a low static friction coefficient is formed over the surface ofthe sheath, new room for improvement becomes obvious.

For example, a boot as a protective member is attached to an end portionof the cable. In this case, the coating film formed over the outermostsurface of the cable and the boot are attached together with anadhesive. However, according to the studies of the present inventors,when the coating film covering the sheath is formed in order to improvethe sliding property of the cable, the adhesion strength between thesheath and the coating film becomes small, and as a result, when bendingpressure is applied to the boot attached to the cable, peeling occurs atthe interface between the sheath and the coating film, and the bootcomes off the cable. In other words, when the coating film with a smallstatic friction coefficient is formed over the surface of the sheath inorder to improve the sliding property of the surface of the cable, theadhesion strength between the sheath and the coating film is smallerthan the bonding strength between the sheath and the boot. As a result,the boot comes off the cable. Therefore, the present embodiment isdevised to suppress the boot from detaching from the cable while formingthe coating film having a small static friction coefficient over thesurface of the sheath. Hereinafter, the technical idea of thisembodiment devised will be described.

<Structure of Cable>

In this embodiment, as one example of the cable, a probe cableconnectable to a medical device will be described.

FIG. 1A is a schematic diagram showing a probe cable 10 connectable toan ultrasonic imaging device. In FIG. 1A, an ultrasonic probe terminal12 to be connected to an ultrasonic probe is attached to one end portionof the probe cable 10 via a boot 11 for protecting this one end portion.On the other hand, a connector 13 to be connected to the main body ofthe ultrasonic imaging device is attached to the other end portion ofthe probe cable 10. FIG. 1B is a cross sectional view of the probe cable10 along A-A line. For example, a plurality of coaxial cables 1 areaccommodated inside the probe cable 10 configured as described above,and a shield 2 is provided so as to cover the plurality of coaxialcables (electric wires) 1. A sheath 20 made of an insulating protectivemember is then provided so as to cover the shield 2. Furthermore, in theprobe cable 10 according to the present embodiment, a coating film 23that covers the above-described sheath 20 and that adheres to the sheath20 is formed. Further, a boot 11 is attached to the probe cable 10 as aprotective member for an end portion of the probe cable 10, via anadhesive 24 provided around the coating film 23. It should be notedthat, in the present embodiment, silicone-based adhesive is used as theadhesive 24, but the present invention is not limited thereto andepoxy-based adhesive and the like may be used.

The sheath 20 is made of, e.g., silicone rubber. On the other hand, inthis embodiment, the coating film covering the sheath 20 is configuredto include, e.g., silicone rubber or chloroprene rubber. In particular,the coating film is configured to include a parent material and fineparticles dispersed in the parent material. Giving one specific example,the coating film includes a parent material made of silicone rubber, andthe fine particles dispersed in the parent material include any one ofsilicone resin fine particles, silicone rubber fine particles, or silicafine particles. Of course, plural kinds may be mixed. It is preferablethat the above-mentioned fine particles have hardness higher than thatof the parent material (e.g., hardness of on the order of 1.1 times ormore in Shore (durometer A) hardness). Note that in the case of siliconerubber fine particles, it may be a spherical powder called so-calledsilicone composite powder in which the surface of a spherical siliconerubber powder is coated with a silicone resin.

Here, the average particle diameter of the fine particles contained inthe coating film is, e.g., 1 μm or more and 10 μm or less. The thicknessof the coating film is then, e.g., 3 μm or more and 100 μm or less. Inthis manner, the probe cable according to the present embodiment isconfigured.

<Producing Method of Cable>

Next, a producing method of the probe cable according to the presentembodiment will be described. First, for example, after an electric wiretypified by a coaxial cable is formed, a plurality (e.g., 100 or more)of the electric wires are bundled together. Then, a shield is formed soas to cover the bundled plural electric wires (shield forming step). Forexample, the shield is composed of a braided shield. The braided shieldis a shield formed by braiding several conductors together and crossingcopper wires. Subsequently, a sheath made of, e.g., silicone rubber isformed so as to cover the shield (sheath forming step). This sheath canbe formed, e.g., by extruding silicone rubber using an extruder.Thereafter, in the present embodiment, a coating film which covers thecircumference of the sheath and which adheres to the sheath is formed(coating film formation step). This coating film can be formed by, e.g.,a dipping method, a spray coating method, a roll coating method, or thelike. At this time, the dipping method is a technique of forming acoating film over the surface of the sheath by pulling up the probecable forming the sheath through the liquid covering material. Thisdipping method is superior to the spray coating method and the rollcoating method in that the film thickness of the coating film formedover the surface of the sheath can be formed uniformly. That is, fromthe viewpoint of improving the film thickness uniformity of the coatingfilm formed over the surface of the sheath, it is preferable to use thedipping method as the method of forming the coating film.

In this embodiment, for example, since the coating film is composed ofthe parent material and the fine particles dispersed in the parentmaterial, the liquid covering material used in the dipping methodcontains the fine particles. At this time, the proportion of the fineparticles contained in the coating film is determined by appropriatelyadjusting the proportion of the fine particles contained in the liquidcovering material. In particular, it is desirable that the weightpercentage of the fine particles contained in the coating film is 10mass % or more and 60 mass % or less by adjusting the proportion of thefine particles contained in the liquid covering material.

Characteristics in Embodiment

<<Features>>

Next, a feature of the present embodiment will be described. The featureof this embodiment is that the coating film having its surface having astatic friction coefficient smaller than the static friction coefficientof the surface of the sheath is formed over the surface of the sheath inorder to suppress stickiness of the surface of the sheath made ofsilicone rubber. As a result, it is possible to inhibit the probe cablefrom being caught due to the stickiness of the surface of the sheath,thereby improving the handleability of the probe cable. In the presentembodiment, the coating film having the following constitution is thenformed over the surface of the sheath, thereby realizing the coatingfilm having its surface having a static friction coefficient smallerthan the static friction coefficient of the surface of the sheath. Thispoint will be explained below.

FIG. 2 is a diagram showing a configuration example in which the coatingfilm is formed over the surface of the sheath 20. The coating film shownin FIG. 2 is composed of a parent material 21. In this case, since thesurface of the coating film (parent material 21) in FIG. 2 is flat(even), the contact area between the coating film and the contactmaterial in contact with the probe cable is equivalent to the contactarea between the sheath 20 and the contact object in the case where thesurface of the sheath 20 is exposed without forming the coating film.This means that static friction coefficient of the coating shown in FIG.2 is equivalent to static friction coefficient of the sheath 20, and itis impossible to realize the constitution “to form the coating filmhaving the surface with a static friction coefficient smaller than thestatic friction coefficient of the surface of the sheath 20” that is thefeature point in this embodiment. That is to say, it is not possible toform the coating film having a static friction coefficient smaller thanthat of the surface of the sheath 20 merely by forming the coating filmmade of the parent material 21 so as to cover the surface of the sheath20. Therefore, the present embodiment is devised to realize the coatingfilm having the surface with the static friction coefficient smallerthan the static friction coefficient of the surface of the sheath 20.

FIG. 3 is a diagram showing a schematic configuration of the coatingfilm in this embodiment. In FIG. 3 , the coating film is formed over thesurface of the sheath 20 of the probe cable. This coating film iscomposed of a parent material 21 and fine particles 22 dispersed in theparent material 21. Since the coating film according to the presentembodiment thus constituted contains a plurality of the fine particles22, as shown in FIG. 3 , an uneven shape due to the presence of the fineparticles 22 is formed over the surface of the coating film. In thiscase, due to the uneven shape of the surface, the contact area betweenthe coating film and the contact material contacting the probe cable issmaller than that of the coating film composed of the parent material 21shown in FIG. 2 . This means that static friction coefficient of thecoating film in which the fine particles 22 are dispersed in the parentmaterial 21 shown in FIG. 3 is smaller than static friction coefficientof only the parent material 21 shown in FIG. 2 . As a result, accordingto the coating film of the present embodiment, it is possible to formthe coating film having the surface with a static friction coefficientsmaller than the static friction coefficient of the surface of thesheath 20. In other words, the roughness of the uneven shape of thesurface of the coating film is larger than the roughness of the unevenshape of the surface of the sheath 20. In this manner, according to theprobe cable having the coating film in this embodiment, it is possibleto suppress the catching of the probe cable due to the stickiness of thesurface of the sheath 20. Thus, according to the first feature point inthe present embodiment, the handleability of the probe cable can beimproved.

Next, the materials constituting the coating film in this embodimentwill be described. The coating film in this embodiment is composed of aparent material 21 and fine particles 22 dispersed in the parentmaterial 21. At this time, the parent material 21 of the coating film ismade of, e.g., silicone rubber. On the other hand, the fine particles 22dispersed in the parent material 21 are configured to include any one ofsilicone rubber fine particles, silicone resin fine particles, or silicafine particles.

Here, differences between silicone rubber, silicone resin and silicawill be described. FIG. 4 is a diagram for explaining the differencesbetween silicone rubber, silicone resin, and silica. In FIG. 4 , themain difference between the silicone rubber and the silicone resin isthe number of reactive groups (e.g., methyl groups) contained in thestructural formula. As shown in FIG. 4 , the number of reactive groupscontained in the structural formula of the silicone rubber is largerthan the number of reactive groups contained in the structural formulaof the silicone resin. On the other hand, the silica contains noreactive group, and the silica is so-called silicon oxide. Here, asshown in FIG. 4 , when the number of reactive groups is large, it hassoft characteristics, whereas as the number of reactive groupsdecreases, it has hard characteristics. The hardness is increased in theorder of the silicone rubber, silicone resin, and silica. On the otherhand, the mass is increased in the order of the silicone rubber,silicone resin, and silica. Here, from the viewpoint of maintaining theuneven shape formed over the surface of the coating film 23, the silicahaving high hardness is most desirable, and the silicone resin isdesirable as the second best. This is because when the contacting objectcomes into contact with the uneven shape of the coating film 23, themore the fine particles 22 have the hard characteristic, the higher theeffect of suppressing the easy deformation of the fine particles 22 dueto the pressing pressure from the contacting material. Therefore, itbecomes easy to prevent the uneven shape of the surface of the coatingfilm 23 caused by the fine particles 22 from gentle relaxation. That is,it is possible to prevent static friction coefficient of the surface ofthe coating film 23 from becoming large due to the gentle relaxation ofthe uneven shape formed over the surface of the coating film 23 and theincrease of the contact area between the coating film 23 and the contactobject.

As described above, the silica has the property of being heavier thanthe silicone rubber and silicone resin. For example, in the dippingmethod described in <Cable Producing Method>, it is necessary touniformly disperse the fine particles 22 in the liquid silicone rubberas a material of the parent material, but due to the heavy weight ofsilica itself, it is sometimes easy to sediment without diffusinguniformly into the liquid silicone rubber as compared with the siliconerubber or the silicone resin lighter than the silica. Therefore, fromthe viewpoint of uniformly dispersing the fine particles 22 in thecoating film 23, fine particles composed of the silicone rubber orsilicone resin are more desirable than fine particles made of thesilica.

From the above, in order to both maintain the uneven shape formed overthe surface of the coating film 23 and make the static frictioncoefficient of the surface of the coating film 23 small and to dispersethe fine particles 22 uniformly in the parent material, the siliconeresin is most desirable as the fine particles 22.

<<Novel Findings>>

Next, findings newly discovered by the inventors will be described. Thefeature of the first embodiment described above is that the coating film23 having its surface with a static friction coefficient smaller thanthe static friction coefficient of the surface of the sheath 20 isformed. As a result, in the probe cable 10 according to the presentembodiment, the coating film 23 is formed so as to cover the surface ofthe sheath 20. This inevitably means that there is an interface betweenthe sheath 20 and the coating film 23. Then, due to the existence of theinterface between the sheath 20 and the coating film 23, the adhesionstrength at the interface between the sheath 20 and the coating film 23becomes manifest as a problem.

For example, a terminal is attached to the end portion of the probecable 10, but in order to protect this terminal, a protective membercalled a boot 11 is attached to the end portion of the probe cable 10.In this case, the probe cable 10 and the boot 11 are bonded togetherwith an adhesive. For example, in a probe cable 10 over which no coatingfilm is formed, the sheath 20 and the boot 11 are bonded together withan adhesive. On the other hand, in the probe cable 10 according to thepresent embodiment, as a result of the coating film 23 covering thesurface of the sheath 20 being formed, the coating film 23 and the boot11 are bonded together with an adhesive. At this time, according to theinvestigation by the present inventors, it has newly been found out thatthe adhesion strength between the sheath 20 and the coating film 23becomes smaller than the bonding strength between the sheath 20 and theboot 11 in the absence of the coating film, so it becomes apparent thatthe boot 11 is detached from the probe cable 10.

Regarding this point, as a result of intensive investigation by thepresent inventors on the cause of the adhesion strength at the interfacebetween the sheath 20 and the coating film 23 being smaller than thebonding strength between the coating film 23 and the boot 11, it hasbeen found that the adhesion strength at the interface between thesheath 20 and the coating film 23 is weakened by the followingmechanism. That is, the parent material 21 constituting the coating film23 is composed of the silicone rubber, but as a result of investigationby the present inventors, for the condensation reaction type siliconerubber coating agent which is generally commonly used, when the siliconerubber is solidified from the liquefied silicone rubber, the gas escapesfrom the silicone rubber, whereby voids are formed in the solidifiedsilicone rubber. For example, FIG. 5 is a schematic diagram showing thatvoids 31 are generated in the silicone rubber constituting the parentmaterial 21 of the coating film 23. As shown in FIG. 5 , as the densityof the voids 31 in the silicone rubber constituting the parent material21 of the coating film 23 increases, many voids 31 also exist at theinterface between the coating film 23 using the silicone rubber as theparent material 21 and the sheath 20. This means that the presence ofthe voids 31 reduces the contact area at the interface between thecoating film 23 and the sheath 20. As a result, the adhesion strength atthe interface between the coating film 23 and the sheath 20 isconsidered to be small.

Then in the probe cable using the condensation reaction type siliconerubber coating agent, it has been inferred that since the coating film23 has the voids 31, the adhesion strength between the sheath 20 and thecoating film 23 decreases, and when the bending pressure is applied tothe boot 11 attached to the probe cable 10, peeling occurs at theinterface between the sheath 20 and the coating film 23 before peelingof the bonded portion of the coating film 23 and the boot 11, and theboot 11 is detached from the probe cable 10. Therefore, it is importantto reduce the void density in the silicone rubber constituting theparent material 21 of the coating film 23 to improve the adhesionstrength between the sheath 20 and the coating film 23. Specifically, asshown in FIG. 6 , when the void density in the silicone rubberconstituting the parent material 21 of the coating film 23 decreases,the voids 31 existing at the interface between the coating film 23 usingthe silicone rubber as the parent material 21 and the sheath 20decrease. This means that the decrease in the contact area at theinterface between the coating film 23 and the sheath 20 is suppressed bythe reduction of the voids 31. As a result, it is considered that theadhesion strength at the interface between the coating film 23 and thesheath 20 can be improved.

In other words, the finding newly discovered by the present inventors isthat if the void density in the silicone rubber constituting the parentmaterial of the coating film 23 can be reduced, the adhesion strengthbetween the sheath 20 and the coating film 23 can be made larger thanthe bonding strength between the coating film 23 and the boot 11.

<<Summary>>

From the above, according to the present embodiment described above, itis possible to prevent the boot 11 from detaching from the probe cable10 while forming the coating film 23 having its surface with a smallerstatic friction coefficient than that of the surface of the sheath 20.That is, according to the probe cable 10 of the present embodiment, itis possible to improve handling of the probe cable 10 and improvereliability of the probe cable 10 at the same time. In particular, thefeature of the present embodiment resides in that the coating film 23having its surface having a static friction coefficient smaller than astatic friction coefficient of the surface of the sheath 20 is formed,and by this feature point, the probe cable 10 having a static frictioncoefficient of the surface of the coating film 23 of 0.5 or less isrealized. In addition, the configuration is realized in which theadhesion strength between the sheath 20 and the coating film 23 is equalto the bonding strength between the coating film 23 and the boot 11, orgreater than the bonding strength between the coating film 23 and theboot 11. Specifically, according to the feature points in thisembodiment, the probe cable 10 having adhesion strength between thesheath 20 and the coating film 23 of 0.30 MPa or more is realized.

<Technical Significance of the Numerical Range>

Next, the technical significance of the numerical range will beexplained. First, the average particle diameter of the fine particles 22contained in the coating film 23 is desirably 1 μm or more and 10 μm orless. It should be noted that “average particle diameter” (averageparticle size) herein means the average particle diameter measured bylaser diffraction method. At this time, when the value is less than thelower limit “1 μm” of the average particle diameter of the fineparticles, the uneven shape formed over the surface of the coating film23 becomes gentle, resulting in a large static friction coefficient ofthe surface of the coating film 23, and the surface stickiness of theprobe cable 10 cannot be eliminated. On the other hand, if it exceeds“10 μm” which is the upper limit value of the average particle diameterof the fine particles 22, as the mass of the fine particles increases,the fine particles 22 sediment, resulting in coating unevenness whenapplying a coating film material to the surface of the sheath by thedipping method. Therefore, from the viewpoint of suppressing the coatingunevenness of the fine particles 22 contained in the coating film 23while ensuring the small static friction coefficient of the surface ofthe coating film 23, it is desirable that the average particle diameterof the fine particles 22 contained in the coating film 23 is 1 μm ormore and 10 μm or less.

Next, the content of the fine particles 22 contained in the coating film23 is desirably not less than 10% by mass and not more than 60% by mass.At this time, when the content of the fine particles 22 is less than thelower limit “10% by mass”, the number of the fine particles 22 becomestoo small and the uneven shape formed over the surface of the coatingfilm 23 cannot be roughened. As a result, static friction coefficient ofthe surface of the coating film becomes large, and the stickiness of thesurface of the probe cable cannot be eliminated. On the other hand, whenthe content of the fine particles 22 exceeds “60 mass %” which is theupper limit value, the coating film 23 becomes brittle. Therefore, fromthe viewpoint of suppressing the brittleness of the coating film 23while ensuring the small static friction coefficient of the surface ofthe coating film 23, the content of the fine particles contained in thecoating film is desirably not less than 10% by mass and not more than60% by mass.

Subsequently, the thickness of the coating film 23 is desirably 3 μm ormore and 100 μm or less. The “thickness of the coating film” herein is athickness of an entire coating film 23 after forming the coating film 23containing the fine particles 22. The average particle diameter of thefine particles 22 is appropriately selected in accordance with thethickness of the coating film 23. At this time, the reason for definingthe thickness of the coating film to be “3 μm” or more is that it isconsidered that even if the surface of the probe cable is wiped off10,000 times, the coating film does not disappear. For example, a probecable used for a medical device may become soiled by adhesion of bloodor the like. In view of frequent wiping off of stains adhering to thesurface of the probe cable, it is also desired that the wipingresistance is excellent. On the other hand, the reason why the thicknessof the coating film is set at “100 μm” or less is that it is consideredthat not only the producing cost will increase but also that theflexibility and the bending property will be deteriorated if thethickness of the coating film 23 is too thick. The average particlediameter of the fine particles to be added to the coating film 23 isselected to be equal to or less than the thickness of the coating film23.

<Verification of Advantageous Effects>

A test probe cable was produced and evaluated in the following manner. Acable produced by twisting 200 coaxial cables having a diameter of about0.25 mm was covered with a braided wire, which was used as a cable core,and a sheath material was extrusion coated at the rate of 5 m/min aroundthe outer circumference thereof with an extruder. Silicone rubber(static friction coefficient: 1.0 or more) was used as the sheathmaterial. Here, as a material of the silicone rubber, KE-541-Umanufactured by Shin-Etsu Chemical Co., Ltd. was used. Other than thistype, addition curable (reaction type) silicone rubbers such asKE-551-U, KE-561-U, KE-571-U, and KE-581-U (all of them are manufacturedby Shin-Etsu Chemical Co., Ltd.) and the like may be used.

After covering the sheath, the surface of the sheath was cleaned, andthen a silicone rubber coating film was formed over the sheath surfaceto produce a cable of Example 1. As the silicone rubber coating agent, acoating solution was produced by selecting an addition reaction typematerial in which byproducts were produced by a curing reaction and hadno volumetric shrinkage. Specifically, 120 parts by mass of siliconeresin fine particles having an average particle diameter of 2 μm (tradename: KMP-590, manufactured by Shin-Etsu Chemical Co., Ltd.), 600 partsby mass of toluene as a viscosity adjusting solvent, 8 parts by mass ofa curing inhibitor (trade name: CAT™, manufactured by Shin-Etsu ChemicalCo., Ltd.) and 0.3 parts by mass of a curing catalyst (trade name:CAT-PL-2, manufactured by Shin-Etsu Chemical Co., Ltd.) were added to100 parts by mass of an addition reaction type silicone rubber coatingagent (trade name: SILMARK™, produced by Shin-Etsu Chemical Co., Ltd.)to produce a solution in which the proportion of the silicone resin fineparticles to the coating film was 54.5% by mass. Next, using thissolution, a silicone rubber coating film was formed over the surface ofthe sheath by a dip coating method (lifting rate: 2 m/s). Thereafter,drying and curing treatment was carried out at a temperature of 150degrees C. for 10 minutes. The film thickness of the produced siliconerubber coating film was about 17 μm. Note that the content of thesilicone resin fine particles in the above coating film was calculatedassuming that the coating agent hardened substantially without mass loss(approximately equal to the blending mass ratio).

Next, as Example 2, 150 parts by mass of silicone resin fine particleshaving an average particle diameter of 2 μm (trade name: KMP-590,manufactured by Shin-Etsu Chemical Co., Ltd.), 600 parts by mass oftoluene as a viscosity adjusting solvent, 8 parts by mass of a curinginhibitor (trade name: CAT™, manufactured by Shin-Etsu Chemical Co.,Ltd.) and 0.3 parts by mass of a curing catalyst (trade name: CAT-PL-2,manufactured by Shin-Etsu Chemical Co., Ltd.) were added to 100 parts bymass of an addition reaction type silicone rubber coating agent (tradename: SILMARK™, produced by Shin-Etsu Chemical Co., Ltd.) to produce asolution in which the proportion of the silicone resin fine particles tothe coating film was 60% by mass.

Note that although SILMARK™ was used as the silicone rubber coatingagent in the above-mentioned Examples 1 and 2, the present invention isnot limited thereto, but it is also possible to use an addition reactiontype coating agent such as trade names: KE-1844, KE-1846, KE-1886,KE-1871 (all thereof produced by Shin-Etsu Chemical Co., Ltd.), or thelike. As the solvent for adjusting the viscosity, aromatic hydrocarbonbased solvents such as benzene, toluene and xylene, aliphatichydrocarbon based solvents such as n-hexane, n-heptane, n-octane,isooctane, nonane, decane, undecane, and dodecane, and the like can beused alone or in combination of two or more.

Subsequently, cables of the reference examples 1 to 3 were produced bychanging the materials of the coating film. The process of forming thecoating film over the surface of the sheath is the same as in Examples 1and 2 above.

In the reference example 1, as the silicone rubber coating material, asolution was produced by adding to 100 parts by mass of a condensationreaction type silicone rubber coating agent (trade name: X-93-1755-1,produced by Shin-Etsu Chemical Co., Ltd.) containing vinyl oxime silane,toluene and n-heptane, 13 parts by mass of silicone resin fine particleshaving an average particle diameter of 2 μm (trade name: KMP-590,available from Shin-Etsu Chemical Co., Ltd.), and in which theproportion of the silicone resin fine particles to the coating film was56.5% by mass. Using this solution, coating was carried out under thesame conditions as in Example 1, followed by drying and curing treatmentat a temperature of 120 degrees C. for 30 minutes. The film thickness ofthe produced silicone rubber coating film was about 15 μm. Note that thecontent of the silicone resin fine particles in the coating film wascalculated assuming that the solid content (nonvolatile content) of thecoating agent was 12% (data value of Shin-Etsu Chemical Co., Ltd.).

In the reference example 2, the conditions were the same as those in theExamples 1 and 2, except the use of a solution produced by adding to 20parts by mass of silicone resin fine particles having an averageparticle diameter of 2 μm (trade name: KMP-590, available from Shin-EtsuChemical Co., Ltd.), and in which the proportion of the silicone resinfine particles to the coating film was 16.7% by mass. The film thicknessof the produced silicone rubber coating film was about 15 μm.

In the reference example 2, the conditions were the same as those in theExamples 1 and 2, except the use of a solution produced by adding to 200parts by mass of silicone resin fine particles having an averageparticle diameter of 2 μm (trade name: KMP-590, available from Shin-EtsuChemical Co., Ltd.), and in which the proportion of the silicone resinfine particles to the coating film was 66.6% by mass. The film thicknessof the produced silicone rubber coating film was about 20 μm.

In the present embodiment, by adopting the above-described featurepoints, the configuration is realized in which the adhesion strengthbetween the sheath and the coating film is 0.30 MPa or more. In thefollowing description, experimental results supporting the fact thatwith this configuration, it is possible to prevent the peeling at theinterface between the sheath and the coating film and the boot fromcoming off the probe cable will be described.

First, the adhesion strength between the sheath and the coating film issubstituted by the following measuring method. FIG. 7 is a diagram forexplaining a method of producing an evaluation sample for evaluating theadhesion strength between the sheath and the coating film. In FIG. 7 , acoating film 51 was formed over a surface of a sheath material sheet 50having a thickness of the order of 1 mm and a width of the order of 25mm, and a boot material sheet 53 having a thickness of the order of 1 mmand a width of the order of 25 mm was bonded to the surface of thecoating film 51 with an adhesive 52. Note that the same silicone rubber(static friction coefficient: 1.0 or more) is used for the sheathmaterial sheet 50 and the boot material sheet 53. As the adhesive 52, acommercially available silicone based adhesive KE-45 (produced byShin-Etsu Chemical Co., Ltd.) was used. The bonding area at this timewas, e.g., 10 mm×25 mm, and the thickness of the adhesive material 52was of the order of 50 μm to 200 μm. The sample for evaluation producedin this manner was left in the atmosphere at 25 degrees C. for 168hours. Thereafter, the tensile shear strength is measured using thesample for evaluation to evaluate the adhesion strength between thesheath material sheet 50 and the coating film. FIG. 8 is a schematicdiagram showing a measuring method for measuring tensile shear strengthusing the sample for evaluation. Specifically, as shown in FIG. 8 ,while holding the respective end portions of the sheath material sheet50 and the boot material sheet 53, the sheath material sheet 50 and theboot material sheet 53 were pulled at a speed of 500 mm/min, and thetensile shear strength was measured to evaluate the adhesion strengthbetween the sheath material sheet 50 and the coating film.

Next, a bending resistance test for examining bending resistance will bedescribed. FIG. 9 is a schematic diagram showing a bending resistancetest of a probe cable. In FIG. 9 , in the bending resistance test, aload of 500 g was applied to the probe cable 60, and the probe cable 60was held in a vertical state. The portion of a boot 61 attached to anend portion of the probe cable 60 is held, and the operations of bendingthis held portion to the right and left by 90 degrees at a speed of 30times/min are performed. Here, the held portion is held in the verticalstate, then bent to the left by 90 degrees, returned to be in thevertical state, then bent to the right by 90 degrees, and returned to bein the vertical state. The number of bendings was 150,000 times or morein total of right and left bendings. In such a bending resistance test,when no peeling or breaking of the boot 61 occurred, it was determinedthat the bending resistance was good (0). On the other hand, when theboot 61 peeled off or broke, the bending resistance was determined aspoor (x).

Further, as to the “tackiness” of the surface, the static frictioncoefficient of the surface of the coating film was smaller than thestatic friction coefficient of the surface of the sheath, moreconcretely, when the static friction coefficient of the surface of thecoating film was 0.5 or less, it was determined as “no tackiness” (o).On the other hand, when the static friction coefficient of the surfaceof the coating film was more than 0.5, it was determined as “tackiness”(x). The static friction coefficient was measured as follows. First, atest sheet 1 having a planar sheet coated with a material to be measuredand having a length of about 10 cm and a width of about 2.5 cm mountedto a flat plate, and a sheet 2 having a 1.5 cm×1.5 cm square planarsheet mounted to a flat plate were prepared. The surface coated with thesheet 2 was brought from above into contact with the surface coated withthe sheet 1 or the surface after the wiping in such a manner that theyfaced each other, and while a load W of 2N was applied from above thesheet 2 flat plate, the flat plate with the sheet 2 was pulledhorizontally with a push-pull gauge, and its pulling force (frictionalforce) F was measured. The static friction coefficient μ was calculatedfrom F=μW.

The measurement results of the adhesion strengths between the sheath andthe coating film, the bending resistances, and the static frictioncoefficients of Examples 1 and 2 and Reference Examples 1 to 3 wereshown in Table 1.

TABLE 1 (Parts by mass if there is no description of unit) ReferenceReference Reference Items Composition Example 1 Example 2 Example 1Example 2 Example 3 Sheath Silicone rubber ¹⁾ 100 100 100 100 100Coating film Parent material Addition reaction 100 100 100 100 typesilicone rubber coating agent ²⁾ Condensation 100 reaction type siliconerubber coating agent ³⁾ Fine particles Silicone resin 120 150 13 20 200fine particles ⁴⁾ Viscosity Toluene 600 600 600 600 adjustment solventCuring inhibitor ⁵⁾ 8 8 8 8 Curing catalyst ⁶⁾ 0.3 0.3 0.3 0.3 Coatingfilm About 17 About 18 About 15 About 15 About 20 thickness (μm) Fineparticles/ 54.5 60.0 56.5 16.7 66.6 coating film ratio (mass %) Staticfriction coefficient of sheath (μ) 1.0 or more 1.0 or more 1.0 or more1.0 or more 1.0 or more Static friction coefficient of coating filmsurface (μ) 0.16 0.14 0.16 1.0 0.13 Adhesion strength between sheath andcoating film (MPa) 0.36 0.30 0.25 0.40 0.20 Surface tackiness ∘ ∘ ∘ x ∘Bending resistance ∘ ∘ x ∘ x ¹⁾ Product Name: KE-541-U (static frictioncoefficient: 1.0 or more), manufactured by Shin-Etsu Chemical Co., Ltd.²⁾ Product Name: SILMARK-TM, manufactured by Shin-Etsu Chemical Co.,Ltd. ³⁾ Product Name: X-93-1755-1, manufactured by Shin-Etsu ChemicalCo., Ltd. ⁴⁾ Product Name: KMP-590 (average particle size: 2 μm),manufactured by Shin-Etsu Chemical Co., Ltd. ⁵⁾ Product Name: CAT-TM,manufactured by Shin-Etsu Chemical Co., Ltd. ⁶⁾ Product Name: CAT-PL-2,manufactured by Shin-Etsu Chemical Co., Ltd.

Table 1 shows that, in the reference example 2 in which the fineparticles/coating film ratio is 16.7 mass %, the bending resistance wasgood (0) but the static friction coefficient of the coating film surfacewas 1.0 which is substantially equal to the static friction coefficientof the sheath surface, and the “tackiness” remained on the coating filmsurface.

In Example 1 in which the adhesion strength between the sheath and thecoating film was 0.36 MPa, the bending resistance was good (0).Similarly, also in Example 2 in which the adhesion strength between thesheath and the coating film was 0.3 MPa, the bending resistance was good(o). On the other hand, in the reference example 1 in which the adhesionstrength between the sheath and the coating film is 0.25 MPa, thebending resistance was poor (x).

In the reference example 3 in which the fine particles/coating filmratio is 66.6 mass %, although the static friction coefficient of thecoating film surface was low, the adhesion strength between the sheathand the coating film was 0.20 MPa which is low, and the bendingresistance was poor (x).

Based on the above experimental results, it is found that the fact thataccording to the constitution in which the adhesion strength between thesheath and the coating film is 0.30 MPa or more, it is possible toprevent the peeling at the interface between the sheath and the coatingfilm and the boot from coming off the probe cable, is supported.

Regarding the coating agent (parent material) of the coating film, asdescribed above, in the case of the condensation reaction type, when thesilicone rubber is solidified from the liquefied silicone rubber, thegas escapes from the silicone rubber, whereby voids are formed in thesolidified silicone rubber. On the other hand, in the case of theaddition reaction type, bubbles are hardly formed in the coating film.Therefore, in Examples 1 and 2 using the addition reaction type coatingagent, it is considered that bubbles in the coating film were lessenedat the interface with the sheath, and the high adhesion strength wasable to be obtained. Note that in Examples 1 and 2, an adhesion strengthof 0.30 MPa or more was obtained without adding an adhesion improversuch as a silane coupling agent. On the other hand, in the referenceexample 1 in which the adhesion was low, an adhesion improver wasfurther added, but no improvement in adhesion was observed.

In the above embodiment, the probe cable connectable to the medicaldevice has been described as an example. However, the technical idea inthe above embodiment is not limited to this, but can be widely appliedto various types of cables that require bending resistance, for example.

For example, it is suitable for cables for applications in which thefriction between cables such as medical cables (endoscope cables,catheter connection cables, etc.) other than probe cables and cabtirecables or the like or between them and a contact object is a problem.

Further, the cable core (electric wire) constituting the cable is notlimited to the coaxial wire (coaxial cable), but may be, for example, anelectric wire in which an insulator is coated around the outercircumference of a conductor made of a single wire or a stranded wiresuch as a pure copper wire or a tin-plated copper wire, or an opticalfiber or the like. Further, the sheath 20 is not limited to siliconerubber, but is not particularly limited as long as it can be used as thesheath material. For example, polyethylene, chlorinated polyethylene,chloroprene rubber are preferred. Further, since it is expected that thediscoloration due to the UV light may be suppressed to some extent byproviding the coating film 23, it is also possible to use the polyvinylchloride as the sheath 20. In particular, the present invention ishighly applicable when the sheath is composed of a material with lowslidability, that is, a material with high frictional force or amaterial with high tackiness. Representative examples are rubbercompositions such as silicone rubber and chloroprene rubber withadhesiveness (stickiness) having a static friction coefficient μ of 0.7or more when used as a sheet base material. The above materials can beused not only alone but also as a composition containing two or morekinds.

To the composition serving as the sheath material, general compoundingagents such as various crosslinking agents, crosslinking catalysts,antioxidants, plasticizers, lubricants, fillers, flame retardants,stabilizers, colorants and the like may be added. The sheath can beprovided by extrusion coating film and, if necessary, crosslinked. Thesheath can also be of a multilayer structure. In this case, when theoutermost layer of the multilayer structure is composed of theabove-mentioned materials, the present invention is highly applicable.

Further, the present invention is also applicable to a medical hollowtube such as a catheter.

FIG. 10A is a cross sectional view of a hollow tube 70 for medical useincluding a hollow tube body 71 and an outer coating film 72 on an outersurface 71 a of the hollow tube body. FIG. 10B is a cross sectional viewof a hollow tube 70 for medical use including a hollow tube body 71 andan inner coating film 73 on an inner surface 71 b of the hollow tubebody 71. FIG. 10C is a cross sectional view of a hollow tube 70 formedical use including a hollow tube body 71, an outer coating film 72 onan outer surface 71 a of the hollow tube body 71 and an inner coatingfilm 73 on an inner surface 71 b of the hollow tube body 71,respectively.

That is, in a hollow tube 70 for medical use comprising a hollow tubebody 71 (made of e.g., silicone rubber), and an outer coating film 72and/or an inner coating film 73 covering the circumference (an outersurface 71 a or an inner surface 71 b, or both surfaces) of the hollowtube body 71 and adhering to the hollow tube body 71, the coating film23 of the embodiment described above can be used as the outer coatingfilm 72 and/or the inner coating film 73, and static frictioncoefficient of the surface of the outer coating film 72 and/or the innercoating film 73 is smaller than static friction coefficient of thesurfaces of the hollow tube body 71, and the adhesion strength betweenthe hollow tube body 71 and the coating film 72 and/or the inner coatingfilm 73 is 0.30 MPa or more. With such a medical hollow tube, sincethere is no “tackiness” on the inner surface or outer surface of thehollow tube 70, when an instrument is used by being inserted into themedical hollow tube such as a catheter for example, it is possible tosmoothly insert and remove the instrument.

Although the invention made by the present inventors has been concretelydescribed based on its embodiments, the present invention is not limitedto the above-mentioned embodiment, and it goes without saying thatvarious modifications can be made without departing from the spiritthereof.

Although the invention has been described with respect to the specificembodiments for complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art which fairly fall within the basic teaching hereinset forth.

What is claimed is:
 1. A hollow tube for medical use, comprising: ahollow tube body; and a coating film covering at least one of an innersurface and an outer surface of the hollow tube body, the coating filmadhering to the hollow tube body, wherein a static friction coefficientof the surface of the coating film is 0.5 or less, wherein an adhesionstrength between the hollow tube body and the coating film is 0.30 MPaor more, wherein a parent material of the coating film is siliconerubber and is produced by curing an addition reaction type coatingagent.
 2. The hollow tube according to claim 1, wherein the coating filmcomprises fine particles dispersed in the parent material.
 3. The hollowtube according to claim 2, wherein the fine particles include any one ora plurality of silicone resin fine particles, silicone rubber fineparticles, or silica fine particles.
 4. The hollow tube according toclaim 2, wherein the fine particles have a higher hardness than that ofthe parent material.
 5. The hollow tube according to claim 3, whereinthe fine particles comprise an average particle diameter of 1 μm or moreand 10 μm or less.
 6. The hollow tube according to claim 1, wherein thecoating film comprises a thickness of 3 μm or more and 100 μm or less.7. The hollow tube according to claim 1, wherein the hollow tube is madeof silicone rubber.
 8. The hollow tube according to claim 1, wherein aroughness of an uneven shape of the surface of the coating film ishigher than a roughness of an uneven shape of the surface of the hollowtube.